Would 1 million faces/vertices be too much for Blender?
1 000 000 faces shouldn't be a problem.
High facecount by itself won't slow down renders very much, this isn't the 90s.
Viewport is slowed down by high memory - face count, high-res textures and complex shaders
Render is slowed down by high light-bounces, HDRIs, and complex shaders (glass, SSS)
To keep memory low (and viewport fast):

link objects, don't append them when building a scene
use lower Subdivision levels for Viewport
use Simplify in Rendertab to lower texture resolution for viewport